Many portable electronic devices, such as cell phones, tablet computers, and multimedia players, usually include circuit boards. Electronic components of a circuit board, such as resistors or capacitors, are usually embedded in a substrate of the circuit board in order to decrease the thickness of the portable electronic device. During manufacturing, the passive components are disposed between two resin layers, and the two resin layers are pressed and connected to each other, thereby embedding the passive components within the two resin layers. However, the electronic components may be damaged when pressed. Therefore, there is room for improvement in the art.